The universal sphere mount relates generally to precision measuring systems that provide for critical detection of light and other radiation from a source, a laser powered tracking system among others, and more specifically to a spherically mounted retro-reflector three-point conical nest mount, having a negative acceptance angle at any rotation of a target upon the invention and the invention defines a target assembly that provides for area and location of the target to a tolerance within +/−0.0005 inch or less. The nest allows a target to rotate about an axis perpendicular to the plane of the nest.
Modern manufacturing technology, particularly that associated with the construction of large composite material structures, such as for aircraft parts machining and aircraft assembly, subjects the contours of components and tooling to accurate measurement and meticulous inspection for compliance with design models and specifications. One manner in which these structures are measured is with the aid of portable coordinate measuring machines such as laser trackers.
Laser trackers measure and inspect large components by illuminating one or more retro-reflecting targets mounted to the parts, tooling, or components in predetermined locations with a laser. The position of the laser tracker and of the positioning of the retro-reflector target is measured using the laser, and compared with design models or specifications, such as those stored on a computer.
Other examples of various measurement systems for reference are as follows. The Global Positioning System, or GPS, is used indoors as a method to precisely set various industrial devices and industrial equipment, including machinery and for close tolerance industrial surveying, as used in manufacturing and assembly operations. Laser projection systems emit a laser beam along a line that represents the position of an edge used in a step of manufacturing, such as the position of a composite lay up sheet.
For reference, retro-reflective photo targets have had countless design adaptations to enhance precision for the various settings and component features that are measured using close range industrial photogrammetry. These adaptations may include straight holes, threaded holes, surfaces, edges, slots and the like. The prior art frequently obtains tolerances as close as +/−0.0005 inch on the various targeting products.
Currently, most spherically mounted retro-reflectors receive incident light through an aperture, then reflect the light to the measuring system for a precise fix of the location of the spherically mounted retro-reflector. When the light source fires, it emits light which is then collected by a spherically mounted retro-reflector and returned for detection by the measuring system. The measuring system then determines the three-dimensional location of the spherically mounted retro-reflectors in the X, Y and Z axes.
To facilitate the use of laser trackers, retro-reflectors are centrally mounted in hollow steel spheres, commonly referred to as Spherically Mounted Retro-reflectors (SMR), which in turn are fitted to the target object in predetermined locations with the use of sphere mounts, such as is shown at in FIG. 1, along with previous designs of the Applicant. The hollow steel balls include a circular opening or aperture in an exterior surface, through which laser light enters the ball and is reflected back along an incident angle to the source by the internally mounted retro-reflector. Surrounding the circular opening or aperture may be a cylindrical hood, configured to reduce or eliminate unwanted glare and to protect the glass optical retro-reflector from breakage. Most sphere mounts are typically cylindrical or disc shaped, and includes a recessed conical nest in one surface which holds and locates the retro-reflector sphere, usually with the aid of a magnet. The opposite surface of the sphere mount is either flat, includes a base shank, or has other possible configurations, that allow for seating within a correspondingly sized bore, or other features, on the target object, permitting the sphere mount to be located at a known position on the target object. A sphere mount having a three-point conical nest, commonly referred to as a kinematic mount, may be utilized.
Conventional sphere mounts accommodate three standard sizes, such as 0.500 inch, 0.875 inch, and 1.500 inch′ and have a hemispherical mounted range of illumination acceptance, generally limited by the mechanical interaction between the edge of the circular opening or aperture in the retro-reflector sphere and the upper surface of a sphere mount. A retro-reflector ball in a conventional sphere mount may rotate through a vertical arc of 180 degrees and may rotate 360 degrees about the central axis within the conical nest of the sphere mount.
In some applications, the laser tracker or illumination source, or the sphere mount itself, may not be disposed within the hemispherical mounted range of illumination acceptance defined by the upper surface of the sphere mount, but rather, slightly below the lower boundary. For these applications, it is known to employ sphere mounts having an axially perpendicular recess between the base of the conical nest and the circumferential perimeter. A retro-reflector ball placed in such a modified sphere mount may rotate through a vertical arc angle greater than 180 degrees when radially aligned with the perpendicular recess by seating the cylindrical hood within the recess, providing an extending illumination acceptance range.
Vertical arc angles of illumination acceptance from 0 degrees to 180 degrees are considered “positive” angles while vertical arc angles of acceptance greater than 180 degrees, that is, below the horizon of the sphere base, are considered “negative” angles. However, a portion of the circular opening or aperture to the ball mounted retro-reflector is occluded by the modified sphere mount, reducing the effective size of the circular opening or aperture and rendering measurement readings more difficult to obtain.